The UK is set to see some warmer temperatures this weekend as the colder than average weather seen so far this April eases its grip.

Temperatures have been steadily climbing since the exceptionally cold weather towards the start of the month, with today through to Friday set to see double-digit figures for many places.

On Saturday temperatures will be generally between 11 and 13 °C, feeling much milder than recent days. However, the weather will be wet, fairly windy and unsettled for many parts – with the best of any drier and brighter weather in the south and east.

Forecast chart for midday Saturday shows low pressure moving in from the Atlantic to bring mild but wet and windy weather for most of the country. High pressure still dominates in the south and east, bringing the best of any drier and brighter weather.

Warmest day of the year so far

Sunday looks set to be the warmest day of 2013 so far, with temperatures expected to be widely in the mid-teens Celsius. While the weather will be slightly more settled than Saturday, many places will see cloudy and breezy conditions with a risk of some light showers.

Once again the south and east will see the best of the weather, with drier and brighter conditions and temperatures of 15-18 °C – with a possibility that some isolated spots could reach around 20 °C.

Leading in to next week temperatures look set to cool slightly, but remain around average for the time of year.

Jet stream shift brings milder weather

The reason for the shift away from the colder weather is the re-alignment of the jet stream, a band of fast moving westerly winds high up in the atmosphere which tends to guide Atlantic weather systems. It’s these weather systems that bring us the mild and unsettled weather we normally expect at this time of year.

During the prolonged cold conditions the jet stream tracked far to the south of the UK, guiding those mild weather systems towards the Mediterranean. The UK, meanwhile, saw an easterly flow – bringing in cold conditions from the cold winter climes of north-east Europe.

Now the jet stream has started to shift its track, moving north to a position more in line with what we’d expect at this time of year. This means we expect to see milder, but also more unsettled weather coming in from the Atlantic over the coming week or so.

Like this:

Fog has affected many areas over the last couple of days, which in some places has been freezing.

Freezing fog forms in the same way as ‘normal’ fog and is typical in winter, aided by clear skies and calm conditions. The cooling of land overnight under clear skies means that any heat radiates back into space cooling the air close to the surface. This reduces the ability of the air to hold moisture, allowing condensation of water vapour into millions of tiny water droplets to occur and fog in to form.

When temperatures are well below freezing, the tiny water droplets suspended in the air are made up of supercooled water droplets – which remain liquid even though the temperature is below freezing. This occurs because the liquid needs a surface to freeze upon, such as a dust or pollution particles. However if there are not enough of these particles about then the water can stay as a liquid.

However droplets from freezing fog can freeze to surfaces on contact, forming rime. Often confused with frost, rime is a rough white deposit formed of feathery ice crystals. It can often be seen on vertical surfaces exposed to the wind – like lamp posts and pylons – as the supercooled water droplets freeze on contact as they drift past.

With warnings in force for fog people are advised to take extra care when driving in affected areas with journeys taking longer than usual. By being ‘weather aware’ our warnings help you prepare, plan and protect yourself from the impacts of severe weather.

Like this:

It seems that it is the time of year for colourful headlines about an impending big freeze. We had them at this time last year, which prompted our Chief Executive to write an opinion piece in The Times.

Now we have very similar stories again, with the front page of the Daily Express declaring ‘Coldest winter freeze on way’ and warning that temperatures are set to plunge as low as -15C.

Some of the stories have taken a cue from parts of our current 30-day forecast. Today’s forecast for 26 November to 10 December reads as follows:

As is usual, there are uncertainties in the forecast for this period, but there are signs that the changeable conditions will continue through the start of this forecast period. There is also a signal for temperatures to be close to or just below the seasonal average. Into December, although there are no strong indications that any particular weather type is going to dominate, on balance colder, drier conditions than at present are favoured, rather than milder, wetter weather, especially across the southern half of the UK.

However, perhaps what the newspapers have failed to pick up on and report to their readers is that there is still a great deal of uncertainty about exactly what weather we will see – as there often is when looking at timescales of over five days ahead.

The science does not exist to make detailed forecasts for temperature and snowfall for the end of this month, let alone for December or even the winter as a whole.

With regards to us ‘briefing the Government on a cold winter’, this is related to our three monthly outlook for contingency planners.

This is a complex product designed to help contingency planners making long-term strategic decisions based on risk exposure. However, it’s not useful for most other people as it doesn’t give one forecast for what’s ahead – rather it outlines potential scenarios and their associated probabilities.

It’s worth noting that while contingency planners use our three month outlook to inform long-term decisions, they make their operational decisions on our five day forecasts and warnings.

These will always provide the best possible guidance on any periods of cold weather, frost or the likelihood of snow, giving detailed local information across the UK.

Ultimately, we’re heading into winter and we expect winter to be colder than the rest of the year – but it’s too early to say exactly what temperatures we can expect or where and when we might see snow.

It’s too early to give forecasts that far ahead, forecasting snow is – after all – a challenge which requires detailed information. While forecasting snow is one challenge, measuring it when it’s on the ground poses another.

There are several reasons for this. First of all snow is subject to the vagaries of the wind and can be blown into deep drifts, leaving bald patches of earth nearby.

Snow also melts, refreezes, and new snow can fall on top. This makes it difficult to discern how much snow has fallen at different times or on different days.

Another tricky aspect of measuring snow is that it often falls on high ground, away from where the majority of the UK population live – and also away from our observation sites.

Snow often falls on high ground but is less common closer to sea-level.

So what do we do to measure this problematic precipitation? In days gone by a manual observer (ie a human being) would go out with a ruler and measure snow on a flat surface.

But this is time consuming, limits observations (as there were relatively few manual observers) and, apparently, became a tricky operation when snow got particularly deep!

So modern technology has given us automated snow sensors which measure snow depth with a laser signal. A piece of artificial turf is the preferred surface below the laser, as it doesn’t grow and therefore doesn’t complicate readings as grass might.

It’s not all that simple though, as even artificial turf can expand and contract according to temperature, as can the soil below it (which can push the artificial turf up or down). Moles can also cause the same problem! To tackle this, our network is under continual review and calibration to make it as accurate as possible.

These fairly technical pieces of kit can’t be placed everywhere, and until last year there were less than 50 spread out across the UK.

Snow depth sensor

This year we have extended our network with 21 new snow sensors, bringing the total up to 68 – you can see the full network on the map below.

Map showing snow sensor network in 2012

This means we can get snow readings from a wider range of locations, which can help our forecasting and is useful for building records and statistics about UK climate.

It’s worth pointing out that while these additions to our observation network are a valuable step forward, the snow sensor network is still relatively sparse in comparison to our UK land weather observation network, which has 463 stations.

Fortunately this is supplemented by observations supplied to the Weather Observations Website (WOW), where anyone can give an up to date measurement of snow or even upload a picture of how much snow they have.

The very nature of our weather here in the UK means that it’s not possible to give precise information for every location in the country, but our network is being continually improved to provide the most detailed, accurate and up-to-date information available.

You can read more about snow and snow forecasts on our dedicated snow pages.

Following a bitterly cold night across eastern England on Friday night, last night was not quite as cold. Friday night saw the lowest temperatures of the winter so far, falling to a biting -15.6C at Holbeach, Lincolnshire. On Saturday night the lowest minimum temperatures were across parts of southern and eastern England. The coldest locations, with values achieved early in the night before cloud amounts increased, were Cavendish: -12.7C Holbeach: -12.4C Cambridge: -12.2C Santon Downham: -11.9C Rothamstead: -11.7C.

Freezing temperatures combined with rain in the north to bring treacherous ice conditions across parts of southern Scotland, northern England and north east Wales last night and this morning as temperatures fell well below freezing across Wales, England and southern Scotland.

However, there was a marked contrast further to the north and west. Milder Atlantic air across northern Scotland and Northern Ireland to the north and west of the rainband straddling the UK resulted in a relatively mild night for mid February.

The coldest place in the UK was Linton on Ouse in North Yorkshire, recording a low of -9.6 °C, whilst at the other end of the scale, Aultbea in Ross and Cromarty, saw temperatures fall no lower than 7.6 °C.

The two tables below show the coldest and mildest spots in the UK last night.

Coldest places in the UK overnight 8 – 9 February 2012

SITE NAME

MIN TEMP (celsius)

AREA

LINTON ON OUSE

-9.6

NORTH YORKSHIRE

TOPCLIFFE

-8.6

NORTH YORKSHIRE

BALA

-7.3

GWYNEDD

PATELEY BRIDGE

-7.0

NORTH YORKSHIRE

SENNYBRIDGE

-6.9

POWYS

WOODFORD

-6.7

CHESHIRE

RAVENSWORTH

-6.7

NORTH YORKSHIRE

CHURCH FENTON

-6.7

NORTH YORKSHIRE

DISHFORTH AIRFIELD

-6.7

NORTH YORKSHIRE

OKEHAMPTON

-6.5

DEVON

LEEMING

-6.4

NORTH YORKSHIRE

TREDEGAR

-6.2

GWENT

BINGLEY

-6.1

WEST YORKSHIRE

GOGERDDAN

-6.1

DYFED

EMLEY MOOR

-6.0

WEST YORKSHIRE

PRESTON MONTFORD

-6.0

SHROPSHIRE

BRADFORD

-5.8

WEST YORKSHIRE

ROCHDALE

-5.7

GREATER MANCHESTER

ALBEMARLE

-5.5

NORTHUMBERLAND

REDESDALE CAMP

-5.4

NORTHUMBERLAND

PENNERLEY

-5.4

SHROPSHIRE

LLYSDINAM

-5.3

POWYS

BRAMHAM

-5.3

WEST YORKSHIRE

BAINBRIDGE

-5.1

NORTH YORKSHIRE

CAPEL CURIG

-5.0

GWYNEDD

Mildest places in the UK overnight 8 – 9 February 2012

SITE NAME

MIN TEMP (celsius)

AREA

AULTBEA

7.6

ROSS & CROMARTY

SOUTH UIST RANGE

6.8

WESTERN ISLES

STORNOWAY AIRPORT

6.7

WESTERN ISLES

KINLOCHEWE

6.6

ROSS & CROMARTY

TIREE

6.3

ARGYLL

ALTNAHARRA

6

SUTHERLAND

BALLYKELLY

5.8

LONDONDERRY

SKYE: LUSA

5.6

WESTERN ISLES

ACHNAGART

5.5

ROSS & CROMARTY

ISLAY: PORT ELLEN

5.5

ARGYLL

MAGILLIGAN

5.5

LONDONDERRY

BALTASOUND

5.3

SHETLAND

FAIR ISLE

5.3

SHETLAND

MURLOUGH

5.3

DOWN

RESALLACH

5.2

SUTHERLAND

MACHRIHANISH

5.2

ARGYLL

CASTLEDERG

5.2

TYRONE

KILLOWEN

5.1

DOWN

BALLYWATTICOCK

5

DOWN

ST ANGELO

4.8

FERMANAGH

KIRKWALL

4.8

ORKNEY

LOCH GLASCARNOCH

4.7

ROSS & CROMARTY

WICK AIRPORT

4.7

CAITHNESS

HELENS BAY

4.6

DOWN

STORMONT CASTLE

4.6

DOWN

The battle between the milder Atlantic air and the very cold air in the southeast continues across the UK, bringing the risk of snow across parts of the country later today and into Friday. Whilst there is uncertainty about where the heaviest and most persistent snow will fall, accumulations of up to 10cm are possible in the worst affected regions. As a result Met Office warnings have been issued and there could be some disruption to travel.

The Met Office is working closely with government departments, contingency planners and transport agencies to make sure they have the best advice available to help them prepare for possible weather impacts.

It was another bitterly cold night across the UK last night, especially across England. The coldest place in England was South Newington, Oxfordshire where temperatures fell to -12.4 deg C, beating last night as the coldest night of the winter so far. In Wales, Tredegar was the coldest spot at -9.5 deg C whilst in Scotland Altnaharra saw temperatures fall as low as -7.2 deg C.